Improvement in telephone-circuits



T. N VAIL. Telephone-Circuits.

No. 222,966. Patented Dec. 23,1879;

BDSTUN.

' each of these districttelephone systems.

UNITED STATES PATENT OFFICE.

THEODORE NLVA IL, OF BOSTON, MASSACHUSETTS.

IMPROVEMENT IN TELEPHONE-CIRCUITS.

Specification forming part of Letters Patent No. 222,966, dated December 23, 1879; application filed September 24, 1879.

To all whom it may concern Be it known that I, THEODORE N. VAlL, of Boston, in the county of Suffolk and State of Massachusetts, have invented a new and useful Improvement in Telephone Circuits, of which the following is a specification, reference being had to the accompanying drawing.

The object of this invention is to prevent the effects of induction upon parallel wires of telephone-lines, and it is especially applicable to the telephone-lines connecting the district-telephone systems of two towns or cities.

It consists in connecting two parallel wires between two district-telephone systems to two grounded circuits in each of these district system s, and in uniting the circuits in one or both of these pairs in such a manner that a metallic circuit is formed whereby the inductive effects upon the two parallel wires are made to neutralize each other in the manner as hereinafter specified.

The accompanying diagramrepresents a part of the district-telephone systems in each oftwo cities connected by parallel wires in such proximity to each other that a current on either of the wires will cause a current on the other wire by induction, and two grounded circuits in each system are shown, which circuits are capable of being connected together so as to form one metallic circuit in the manner which I shall show and describe in another application for a patent of the United States. In that application will be described a suitable device for effecting this result, which device may be used in carrying this invention into effect.

It consists of a polarized tongue, B, operated from the central office, to make and break an earth connection, but any other device which will accomplish the same result may be used.

O O are the central offices in two cities-as, for instance, in Lowell and Boston. 1 and 2 are two parallel wires connecting these central offices. a and b are two grounded circuits in 1 2 3 4 are stations on these circuits; and M is the electro-magnet for connecting these circuits so that they will form one metallic circuit. The telephone and signal bell connections are not shown, for thereason that any suitable system may be adopted.

In the Boston-system the circuits to and b are shown as each having an earth termination, one circuit, a, passing through the magnet M to the polarized tongue B, and thence to earth, and the other circuit, 1), passing direct to the tongue B, and thence to earth.

In the Lowell system the earth-connection with the tongue B is shown as broken, and the two circuits 0. and b as connected metallically; but the grounded circuits in either system may be made into one metallic circuit, as may be desired, or the circuits in both systems may both be made into one metallic circuit at the same time.

If any station in one city-as, for instance, station 1 in Boston--wishes to communicate with any station in the other city--as, for instance, with station 1 in Lowell-the central oflice in Lowell is notified from Boston, and circuits a and bin Lowell are then united into one metallic circuit by the magnet M by breaking the groundconnection. Oireuitsa in both cities are connected to the wire 1, and circuits 1; in both cities are connected to the wire 2, and consequently the'current sent from station 1 in Boston will pass to station 1 in Lowell by the.

wire 1, and will return to Boston by the wire 2.

As both wires are simultaneously carrying the same current the induction caused by the current on one wire will be neutralized by the induction caused by the current on the other wire, and therefore other parallel wires will not be affected, and the wires 1 and 2, being joined metallically, will not be affected by ourrents on other parallel wires .or by earth-currents.

Instead of two circuits passing through different stations there may be two circuits pass-.

ing through the same stations, in which case these two circuits can be united at any station, so as to form a metallic circuit.

I am aware that it is not new to prevent the effects of induction in telephone-lines by the use of metallic circuits, and this I do not claim as my invention; but

What I do claim, and desire to secure by Letters Patent of the United States, is--.

The combination, with two parallel Wires ing connected to the other of said parallel connecting the central offices of two districtwires, substantially as and for the purpose set telephone systems, of a series of grounded cirforth. cuits in each system, capable .of being con- In witness whereof I have hereunto signed nected in pairs at any point, so that each pair my name. forms one metallic circuit and one centraloffice terminal in each pair, capable of being connected to one of the parallel wires connect- Witnesses: ing' the central offices, and the other central- ALEX. L. HAYES, office terminal of the same pair, capable of be- 0. E. MADDEN.

THEODORE N. VAIL. 

